PROJECT SUMMARY/ABSTRACT This Mentored Clinical Scientist Research Career Development Award proposal describes a five-year research and career development training plan for Dr. Jessica Garbern to establish an independent research career in cardiac regeneration. Dr. Garbern aims to become a physician-scientist developing cellular therapies to regenerate and restore damaged cardiac tissue to treat pediatric heart failure and congenital heart disease. Dr. Garbern will be primarily mentored by Dr. Richard Lee, Professor in the Department of Stem Cell and Regenerative Biology at Harvard University, internationally recognized for his work studying heart regeneration, and co-mentored by Dr. David Mooney, Professor of Bioengineering at Harvard University, internationally recognized for his work in tissue engineering. Through the research plan, didactic experiences, and structured mentorship described in this proposal, Dr. Garbern will combine her prior background in biomaterials, molecular biology, and physiology with new skills in gene editing of induced pluripotent stem cells (iPSCs), immunology, and nanotechnology to test whether strategies to alter expression of human leukocyte antigens (HLA) will render iPSC-derived CMs hypoimmunogenic. The adult mammalian heart has a very limited ability to regenerate, and multiple strategies have been proposed to develop cell-based therapies for heart failure. To be clinically viable, such strategies must overcome barriers produced by the immune system to promote regeneration and prevent rejection of transplanted cells while avoiding the complications of chronic immunosuppression seen following heart transplant. Allogeneic CMs derived from iPSCs capable of evading the host immune system could potentially eliminate the need for immunosuppression while also be available for immediate use. Human leukocyte antigens (HLA) are cell surface proteins that allow the body to recognize foreign cells. Removal of selected HLA proteins on iPSCs that are then differentiated into CMs may prevent immune rejection of transplanted cells. In Specific Aim 1, Dr. Garbern will test the hypothesis that CMs derived from HLA-deficient iPSCs avoid T cell activation and immune rejection in vitro and in vivo. Removal of selected HLA proteins from iPSCs will be performed using CRISPR gene editing technology. Alternatively, immunomodulatory biomaterials designed to suppress the host immune response might minimize the need for immunosuppression after cell transplantation. In Specific Aim 2, Dr. Garbern will test the hypothesis that bioengineered nanoparticles capable of delivery of RNA interference to selected HLA genes will inhibit T cell activation in vitro. Through the career development activities described in this proposal, Dr. Garbern will build upon her foundations in engineering, biology and medicine to become a leader in overcoming immune barriers to transplantation of iPSC-derived CMs.